Databases may be distributed among multiple physical nodes. Sharding refers to the horizontal partitioning of a database among multiple physical data stores. In relational database management systems, data is organized into tables containing rows and columns. Each row corresponds to an instance of a data item, and each column corresponds to an attribute for the data item. Sharding produces partitions by rows instead of columns. Through partitioning, the data in a single table may be spread among potentially many different physical data stores, thereby improving scalability.